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6,945 Posts
Discussion Starter #1 (Edited)
Been slacking on this when I told lots of people Id do a small write up. But a thread this morning made me decide to do it lol

As many of you may know, I have a 2004 3.8 Mustang I have made a HCI N/A build 4.2. I have also installed a 3200 Revmax Stall and did the home Jmod shift kit. I still have not taken it back to my dyno tuner to fix the shift points that are slightly off now. I believe the stall has thrown them off a hair. But when I do get a good shift in I can tell it is much firmer then before. But I also have the shift pressure increase w/ the tune.

Now if many of you are like me, digging off into major items like a tranny or engine for the first time is nerve racking. Especially if its your Daily Driver !!!! Mess it up and your screwed !!! So I like to do as much researching as I can before I get into something like this. And I did. I finally found a decent write up with some really good pictures and it made me 10x more comfortable doing the Jmod. I cant remember all the bolt sizes or how many, but that really doesn't matter that much, common sense will tell you what size sockets to use ..... though the write I used has sizes and what not to help you. But every situation is different, like I said I was doing a stall swap also.

For those of you wondering, the Jmod is named after Jerry, one of the Ford founders of the 4r70w. He designed/released the tech info and it then became known as the "Jmod" after its creator. It is a shift kit specced by him, just like any other. Other brands will be differently specced and may have more/less parts to add or take out or replace.

Now the original tech article for the Jmod and and building a 4R70W tranny can be found on the TCCoA forumshere

But these instructions were written for the early/mid 90's model that was much worse then the later models. A revised edition for us can be found here

The write up I found to greatly help me before starting this project is here

With this all linked, especially the late model revised edition, you can easily do this yourself. But reading all those fancy words can get confusing if you dont know what your looking at, so Ill help you with that.

*keep in mind its been 3 months since Ive done this, detail wont be 100%* And my engine was out and you'll see where my mid pipe is still hanging w/ long tubes out of the way

All I had to purchase was:
Tranny fluid recommended by Ford
Tranny Fluid Filter
And the 2 gaskets from my Ford Dealer. IIRC they were like 5$ for both.
All required tools and other products I already had, or had access to.

Please do not rely on this thread to do your Jmod, this will assist you, but do refer to the links provided, and do your own research as needed to complete.

Lets Begin:

First off, as many instructions say, disconnect your neg(-) battery terminal. You will be working with electrical parts during this and do not want to ruin any of them.

The work area is a very tight fit, so to make this easier, through most of this I had the front end raised as high as my jack stands would allow. Always use them, do not trust a jack only to hold the car up. But to help even more I raised the rear of the car up as well and put it on stands.

Their is a 99% chance you will be spilling auto tranny fluid (atf) on the ground during this so if you want to lay something under you ( i had an old blanket ) then do it now.

Ive heard some people unhook the tranny oil cooler line that goes to your radiator and run the fluid out with the car running through it. But then your just heating things up and having to wait for things to cool ... My way was messy, but its gonna happen like it or not. Their is NO drain plug ... why idk ... thank you Ford.

So get the socket/ratchet/extensions you need and begin to loosen the oil pan bolts. I suggest loosening them all a few thread, and then working on only one half. This way the pan will tilt on one end to let the fluid pour out. The pan may stick, so before you go very far, break it loose. I got a bit ahead of myself before taking pics, so I held the pan up in the position with some tilt to show you how to drain it:

Let the pan down slowly, it will be full of oil and you dont want to spill it, I did this by myself and made a bit of a mess but a second person would help A LOT !!!

*For a fun fact: ATF is red in color. When dropping the pan I spilled it all down my arm. SO I played a trick, I went to the front door, my mom was on the other side of the house, yelled at her to come here quick. Just enough to get her their quick, but not in such a voice to freak her the hell out and come running lol When she comes around the corner I was holding my upper arm and saying I cut myself under the car and she see's this:


Back to business:

Once you have the pan off and out of the way, pour out the oil. This is what you'll see:

Pull out the old filter.

and you'll see the bottom of the valve body(vb) and the electrical strip (some had actual wires)

Pull off the electrical connections. The strip is plastic and the connections were on pretty tight, so be careful doing so. Dont wanna snap it.

In the same picture towards the bottom about mid way, you'll see a piece with "spike" points, I believe in the late model revised write up this part is the "rooster comb".

Just above it you can see a piston sticking out, and a shaft fits into it coming off the rooster comb. When reinstalling that shaft, the piston must line up the exact same way. When you shift the gears in the car, it moves this piece, controlling that piston's position.

Another angle

Remove the lever holding it in position by its one bolt

Their are two different size length bolts holding the vb in. Obviously those need to go back in the same spot, and it'll be obvious which ones go where.
Also their are two different size heads. 8mm and 10mm. Your only worried about the 8mm ones.
I started by removing the outside bolts:

Next remove the inner bolts, leave the middle one in. All of the weight of the VB will be held by that one bolt, but FYI their is a tone of AFT waiting to fall on your head once the VB is removed. So get your oil pan again, then slowing start dropping the VB by that one bolt. I do recommend you break it loose first, finger tighten again before your drop the VB. Will make it easier. Its not to heavy but holding it up with one hand and loosening that middle bolt and keep it in place somewhat so you dont have a shower of ATF is tricky alone.

Some parts will fall out one you drop the VB. Dont worry, you'll fetch those out of the oil later.

Once the VB is out you'll see this:

The VB Out, looking from the top side, w/ the top side gasket off:

The old gasket needs to be scrapped off, but we are talking a very very thin gasket, so try not to cut into the metal surface so the new one will seal well.

Next you see the circle plates. Some have 3, others have only 2. Mine obviously had two.

These plates must go back in the same position. So instructions say mark their positions.

Once done, you can remove the plates, you'll see why position is important here with the plate off:

Now here you must be very careful with the VB. Once the next plate is removed, several small metal balls that control fluid flow will be able to fall out. Avoid this by not turning the VB upside down lol

Next remove the top plate, this is the separator plate. Remove it. This plate is what you'll be drilling in to for the new specs. The second gasket is beneath the plate. Lift the plate off, and remove the old gasket.

Location of the metal balls for the valves:

Once the plate is removed. Clean it, and mark the holes according to the chart in the tech notes. You'll see the picture on page 2 here

The instructions at the revised link will tell you which holes to drill out, and what size drill to use.

Based on the late model revised instructions, the holes should equal:

#2 .100-.110
#4 .100-.110
#5 .100-.110
#9 .100-.110
#10 .093
#11 .100-.110

During this I also did some research on my own to compare:

Measured out my current 1-11 holes and compared stock to the 97 300+hp, and 98+ Jmod instructions.

2004 V6 Mustang 4r70w Jmod Holes

2004(Stock): '97 300hp+: '98+ Jmod:
1 = .172 None ---
2 = .078 .100 .110
3 = .187 .180 ---
4 = .078 .100 .110
5 = .078 .081 .110
6 = .140 .125 ---
7 = .078 .125 ---
8 = .250 None ---
9 = .078 .089 .110
10 = .078 .089 .093
11 = .109 .089 .110

As you can see, the stock later models are will equipped compared to the older versions. Remember that 97' 300hp is what you drill them to, so they started even less. And some of my stock holes were already bigger or close to the same size.

Be sure that after drilling, if any of the holes you drilled out have sharp edges point out you need to burr them down. I had some small pointed sanding stones on a drill adapter to do this with myself. What ever works for you though.

Now I had forgotten to take any pictures of the process of taking out the accumulator springs. But I will be stealing some pics to save you from going from link to link from the write up I linked earlier.

You now must remove the needed springs. I believe some had already fallen out when pulling out the VB. I cant not remember a bunch of detail here. So referring to my links will help alot.

The write I follow the man used a bottle jack. I used the same concept with my floor jack, and used a 1/2'' extension about 8'' long to lift up and remove the snap rings.

Now you are working on this for the 1-2 shift, so follow this key to find the correct cylinder to lift on:

Now I had a friend bring me a selection of snap ring pliers from his work with different angles on the tips, so it helped having those to get those rings out!

Once out, remove the springs and replace the cap, compress, and replace the snap ring.

The other 2-3 springs may have fallen earlier, along with the cap that hold them in. That cap needs to be replaced. If the entire accumulator fell out along w/ the upper spring, it must be replaced.

Here are the springs that were removed, along w/ a yellow plunger that will have been sitting in the tranny oil pan when removing it. It will be thrown away.

as you can see here, I have put a smaller blue spring inside of the yellow spring. IIRC, this was the 1-2 springs set up. It came out just like that.

With everything replaced. Its time for the reinstall. The VB must be put back together with the new gaskets in place.

Now when the VB was dropped. A small white filter w/ a black bracket on it may have fallen out. No worries. It must go back into position. For this you need some Vaseline, it will allow it to stick into place and is compatible w/ ATF.

You can see the shape of the flat end and where it meets on the tranny:

And here it is in place:

Your almost done !!!

Time to put it all back together !

Please remember their are moving parts, clutches, and metal in a transmission. You dont want dirt/debris in your engine do you ? Nope, so dont let it get into the tranny!!!! I used some carb cleaner to spray and wiped things down the best I could. I did this over a couple of days so Im sure some wind was blowing dirt around.

W/ the VB back togeter and the upper gasket on put it back into place. (Remember that piston must go back in the same position against the shaft sticking out from the rooster comb. Make sure its aligned correctly!) start that middle bolt back to keep it up. Start all the rest of your bolts and remember their are long and short bolts. The other write up has a chart of the locations:

Replace all these bolts and tighten in the specified order. I would not use anything bigger then a 1/4 ratchet for this. those gaskets are then and you dont want to tq them to much. snug will be fine im sure. I dont have an 1''/lb tq wrench is why I say to do it that way.

Almost done!

Replace the electrical connectors

Now put in the new filter, be sure to lube the rubber ring w/ some atf oil to help it slide into place.

Now I did have some trouble here. I couldn't get the filter to go all the way up into place ... so I used that floor jack again to help put some pressure on it and it went in. Have a slight dent in the filter cause of that too -_- Oh well it worked.

Your done with the internals !

Take the tranny oil pan, I cleaned mine out well, it had a lot of grit on it from the clutches and their is a magnet on the pan. I cleaned as much of it off as possible.

Now clean off the gasket surface of both the tranny housing and the tranny oil pan. As well as the gasket. I used carb cleaner and wiped it all down well. Place the gasket on the pan and place it into position. Tighten bolts. Their is no specific order on these bolts, But I tried to go to the opposite bolt each time. This way all bolts tighten evenly. Same concept as tightening lug nuts on your wheels. If you tight them all side by side, one area might be looser then the last place you tightened. I went around like that 3-4 times to make sure all were tight.

All is set now. Replace the tranny fluid. If you happen to know how much you lost during this. Thats how much you replace. A friend of mine that has just done a VERY similar build, stall and all. Told me it took him about 8qts to refill. So thats what I bought and used. Sure enough it worked for me! I had done this after the new stall was in. I also poured as much fluid as I could in the new stall before hand. So Im not truely sure how much you'll lose doing just this Jmod.

Their is a dipstick in the engine bay. Once you have replaced about how much you lost. its time to get the fluid stirring. Double check everything to make sure its not going to leak. Let the car down off the jacks. Replace neg(-) battery cable start the car. As the engine turns, it turns the stall. This will pump the fluid. But you must fill all the cavities w/ fluid. So you need to go through all the gears a few times to make sure they ALL fill w/ fluid. I backed up and down the drive way 5-6 times and check the fluid w/ the engine running. I filled it to the full mark doing this. Then I went and drove it around the block a few times to make sure I was using 3rd gear and 4th (O/D). Once I returned, I check fluid level and topped it off to full. Over the next few days I kept check the fluid. Never needed any, but dont skip this. Running to much or not enough fluid can cause failure !!!!

And btw, be nice to it, while your driving around to get fluid into the 3rd/4th gears. Dont test the Jmod out yet, thats part of the not enough fluid failure comment. Wait till your sure everything is properly running and working...

I do not take credit for the instructions of this write up. Info was gathered off the links provided and sub links from them. I search on forums and through google for all my information. Many of the pictures shown here are from my car, but not all pictures. I followed the directions provided at the other links with personal success with out complications. I can not guaranty that this is the same for everyone, and will work in your case. I do not take responsibility for anything that occurs, or injuries, in anyone else’s situation. As stated in the first of thread, this "write up"/"How To" is not perfect. It is not meant to be the only source of instruction on this mod. Please refer to the links provided and do your own research if needed.

Thank You. I hope this helps you proceed into the decision of doing the Jmod shift kit. Good Luck!

Raging Mad Motherfucker
1,050 Posts
Awesome! I've been looking for something a little more in depth than the ones you linked. +reps

STICKY??? :yes

6,945 Posts
Discussion Starter #5
how long did this take you ? (the jmod, not the writeup)
well due to weather, and work, and not having the drill bits at my house, and having to get the snap ring pliers from a friend. I did it over like 3-5 days or so.
Plus I speant time measuring and comparing ****. And was working on the stall about that time also. I was having issues getting the stall in, and getting the engine to mate correctly to it. So when My friend brought those pliers, I pull the snap ring out, got the springs out, and installed it and thats all I did with it that day. Speant the rest of it with him helping me on that engine/stall. But taking those springs out took a whole 5 minutes. And took that long mostly cause I tried 3 different types of pliers before I found the right size/angle lol

But if you had all the needed supplies, you could do this in an afternoon by yourself I think.

975 Posts
I was going to mike but the tranny went out on my '00 v6 and I couldn't swing the money to fix it so I had to trade in. to this day how does the j-mod feel in your car.

6,945 Posts
Discussion Starter #16
Well today it feels nothing ... the car was side swipped sitting outside my house. Drove across the whole driver side.
And I just started back to school full time. So the repairs have been slow.


I must say.
She continues to shift firm and fast. Between this and the increases from the tune. It feels amazing at WOT.

---------- Post added at 04:36 PM ---------- Previous post was at 04:35 PM ----------

Here is a race I did on 100 shot of nitrous.

You can see how quickly the rpm shifts


683 Posts
I used it as a reference for doing mine. I really wish this tuning headache I have would just ****ing go away and I could feel the difference my M90 *should* be making too...

*EDIT* Also, this write up is what made me decide to do Jmod

Was str8chillng
506 Posts
7/64ths drill bit on all the holes. Holes 2,3,4,5,9,10,11. Remove upper and lower spring in 1-2 and remove bottom spring from 2-3. Drop overdrive accumulator and use weaker yellow spring from 1997 ford mustang, makes harder engagement.

especially with the 1-2. you might want to keep your springs in there.

tl;dr this is my guide simplified. rizzo has a good instructional video on youtube if this guide was incomplete.
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